No matter what humans do, it seems that bacteria have an answer. They resist our antibiotics, thrive in our placentas and even eat our oil spills. This evolving bacterial menagerie can cause us many problems, but it may also provide some solutions. Now, a bacterium that eats our drug waste could help stave off our addictions.

Lei Fang and Colleagues at the University of Kentucky in Lexington have carefully altered the structure of an enzyme the bacteria produce: cocaine esterase. The new prote...